Whole sections of current sewer systems in Europe are in need of replacement due to corrosion, sinking or other damages of leaking sewer pipes and as a consequence of undersizing, because in many cases original planning of housing development and the volume of sewerage per inhabitant were insufficient for the later development.
To replace such sewer pipe, there exists a press pipe tunnelling process, in which pits or manholes are excavated at intervals of about 60 or more meters along the sewer pipe at existing inspection chambers or inspection chambers to be built (DE-OS No. 36 20 026). Starting from a manhole, a cutter head is advanced along the pipe to be replaced. A pivot bearing of the cutter head is mounted on the front end of a pipe segment of the new sewer pipe. The new pipe is pressed forward by means of the cylinder units with the cutter head starting from the manhole in the direction of the pipe to be replaced. Other product pipes are attached in succession on the rear end of the new pipe segment. This procedure has the advantage that the sewer pipe to be replaced does not have to be exposed over its entire length, so that the obstruction to traffic is less grave.
Of course, this known device has difficulties with the working of reinforced concrete pipes and the guidance of the cutter head. It is often desired to run the new pipe on the same level as the old pipe. If the new pipe has a larger diameter, its axis is, therefore, higher than that of the old pipe. In addition, sewer pipes are frequently cemented into the ground, whereby the thickness of the concrete usually fluctuates over the circumference. At the top, for example, thickness is the thinnest.
Both of the aforementioned circumstances cause the prior art device to shift slightly to the side or to the top. Thereafter, a radial misalignment of the cutter head hardly can be corrected.